Photomasks, reticles and the like are typically protected from particulate contamination during fabrication by a pellicle which forms a hermetic seal around the patterns on photomask. The pellicle isolates the photomask pattern and the focal plane of the pattern from ambient dust or other foreign particles, ensuring such foreign substances are not reproduced on the semiconductor wafer during transfer of the photomask pattern to the substrate. Generally, the pellicle includes a thin protective optical membrane or film stretched across a rigid peripheral frame which may be mounted to the surface of the photomask. The pellicle film has transmissive properties which allow the passage of ultraviolet light, electromagnetic radiation and the like when the pelliclized photomask is used in the fabrication of integrated circuits. The pellicle isolates the photomask pattern from dust or other foreign matter during fabrication, and is often left on the photomask to provide continuous protection against the collection of such contaminants when the photomask is not in use.
In addition to protecting the photomask from particulate contamination, the hermetic seal between the pellicle and the photomask prevents the exchange of gases between the atmosphere and the interior cavity beneath the pellicle. When the covered photomask is subjected to changes in temperature or pressure such as when the photomask is transported to a different altitude, the difference in pressure between the interior cavity between the pellicle and the photomask and the atmosphere outside of the pellicle may rupture or damage the protective membrane. When the pellicle membrane ruptures, the photomask may be exposed to dust and other foreign particles in the environment as well as pieces of the ruptured pellicle. A pellicle which provides for the exchange of gases between the interior cavity beneath the pellicle and the atmosphere without introducing particulate matter to the photomask pattern would allow the pressure within the interior cavity to equalize with the atmosphere, preventing rupture or damage of the pellicle membrane.
U.S. Pat. No. 4,833,051 discloses a pellicle frame with a vent in the form of a hole extending through the frame and a filter optionally covering the hole. U.S. Pat. No. 5,344,677 to Hong discloses a pellicle having a longitudinally extending channel. A first opening connects the channel with the interior of the pellicle while a second opening contacts the other end of the channel with the atmosphere surrounding the pellicle. A vent structure which provides for the exchange of gaseous substances between the interior and exterior of the pellicle while isolating the interior cavity beneath the protective film from particulate contamination is desirable. Furthermore, a pellicle with a vent structure which may be efficiently manufactured is also desirable.